Higher comfort, electric power saving and durability have been sought for the motors of household electrical appliances and information appliances, such as brushless motors, fan motors and the like. Especially, for the bearings of the small motors used in the household electrical appliances, a grease composition is required to have low noise performance and acoustic long life.
A grease composition is disclosed which is designed to achieve the low noise performance and the acoustic long life by adding a detergent dispersant to the grease composition to prevent the wear debris caused by running-in wear from adhering to the rolling surfaces (JP4117445B). There is disclosed another grease composition that is designed to upgrade the initial acoustic property and also prevent the acoustic property from deteriorating with the passage of time and under the conditions of high temperatures by using a urea based thickener having a particular composition in combination with a particular organic sulfonate (JP 2008-143979 A).
However, the demand for improvement in the acoustic life under the conditions of high temperatures has still been increasing with respect to the rolling bearings incorporated into the small motors for the household electrical appliances and information appliances.